Apparatus and method for setting a tubing anchor and tensioning tubing string thereabove

ABSTRACT

A tensioning tool for connection with a tubing hanger and tubing string suspended from the tubing hanger retained in a dognut by a hanger retainer. Preferably the hanger retainer is temporarily engaged to the top of the tensioning pup for release therefrom once a lower end of the tubing has been fixed by a tubing anchor and the tubing has been lifted a tensioning distance. The hanger retainer is then engaged with the tubing hanger for suspending the tensioned tubing from the dognut locked in the wellhead. The dognut and the hanger retainer have co-operating locking faces which prevent rotation of the hanger retainer in the dognut once the locking faces are mated which assists in maintaining torque applied to the tubing string which may have been applied to rotationally set the tubing anchor. More preferably, the tensioning pup has a series of gradations marked on the pup for measuring the amount of tension applied to the tubing string.

CROSS REFERENCE TO RELATED APPLICATION

This application is a regular application claiming priority of U.S.Provisional Patent application Ser. No. 60/574,203 filed on May 26,2004, the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

Embodiments of the invention relate to production of oil and gas from awellbore and more particularly to apparatus for tensioning productiontubing to prevent wear due to compression of at least a portion of thetubing string during production.

BACKGROUND OF THE INVENTION

In conventional oil and gas production, once a wellbore has beendrilled, cased and perforated, a production tubing string is loweredinto the wellbore to produce the hydrocarbons therethrough. A rod stringextends through the production tubing string to either a reciprocatingpump or a progressive cavity pump (PCP), positioned at a downhole end ofthe production tubing. In the case of a PCP, the rod string is used torotate a rotor within a stator in the PC pump, to pump the hydrocarbonsto surface. A top drive is typically used to rotate the rod string. Inthe case of a reciprocating pump, the rod string is reciprocated axiallywithin the tubing string, typically by a pumpjack. Further, in the caseof the reciprocating pump, an anchor is set at the lower end of theproduction tubing to prevent a corresponding axial movement of the pumpbarrel during reciprocation of the rod string.

The length of the production tubing may be greater than 1000 ft and,more typically, is at least 3000-4000 ft long, depending upon the depthof the wellbore. Typically, the weight of the tubing string hanging inthe wellbore places at least the portion of the tubing string closest tosurface, in tension. In such long strings of jointed tubing andparticularly when using a reciprocating pump, it is not unusual that theproduction tubing string closest to the tubing anchor rests on theanchored pump barrel causing a portion of the tubing string to go intocompression and buckle slightly. Buckling of the tubing string mayresult in contact with the rod string resulting in wear as the rodstring is actuated. Excessive wear may eventually compromise thestructural integrity of the production tubing necessitating frequentreplacement. Tripping the production tubing string in and out of thewellbore to effect said replacements results in cessation of productionand costly downtime and servicing.

Typically, the tubing string may be tensioned approximately 1 inch forevery one thousand feet of tubing in order to alleviate buckling.Conventional methods of tensioning tubing include lowering the tubingstring to a desired depth, setting a tubing anchor at a lower end of thetubing to fix the position of the lower end of the tubing string andthen pulling up to stretch the tubing. Once the tubing is stretched, aset of shorty slips are used to hold the tubing string in place. Thepulling apparatus is disconnected so that a dognut can be threaded ontothe tubing string. The pulling apparatus must then be reinserted inorder to lift the tubing string to release the shorty slips. The tubingstring must be lifted at least 3 inches, and more typically 5-6 inchesto effectively release the shorty slips. In the case of shallow wells,there is not enough stretch in the tubing string to permit sufficientlifting and therefore attempts to straighten the tubing may result intearing out the threaded joints.

Further, even in deeper wellbores where there is sufficient slack topermit lifting high enough to set and release the slips, the methods arefairly crude and inaccurate and do not always have a successful outcome,the tubing string being tensioned too much or not enough.

SUMMARY OF THE INVENTION

In one embodiment, a tensioning tool engages a form of tubing hanger,hanger retainer and dognut from which a tubing string is suspended, topermit lowering of the tubing, setting of a tubing anchor and lifting ofthe tubing hanger and tubing string to be stretched or tensioned.Measuring means are provide to determine a tensioning distance to whichthe tubing string and hanger are lowered such that when lifted, adequatetensioning of the tubing is achieved without over-stretching the tubing.A retainer is provided for engaging between the tubing hanger and thedognut, lockingly supported in a wellhead bowl, for supporting thetubing string in the dognut following tensioning of the tubing string.The form of tubing hanger and retainer minimize over tensioning andenable support and anti-rotation of the tubing hanger and tubing string.

Preferably, the tool comprises a tensioning pup that engages the tubinghanger and which is marked with a series of evenly spaced gradations formeasuring the tensioning distance. A hanger retainer or nut is engagedwith a top of the tubing hanger once the tubing has been tensionedpermitting the tensioned tubing to be suspended from the hanger nut inthe dognut.

In the case where the tubing anchor is rotationally set, at least someof the torque applied to the tubing string to set the anchor ismaintained by the tubing hanger and retainer in order to keep the tubinganchor actuated. Mating circumferential locking faces are machined on aninner radial face of the dognut and an outer face of the hanger retainerwhich, when aligned and mated, rotationally lock the hanger nut in thedognut preventing release of at least some of the torque applied to thetubing string.

Thus in a broad aspect of the invention a tensioning tool for tensioninga tubing string suspended in a wellbore casing by a tubing hangersupported in a dognut in a wellhead and anchored at a downhole end by atubing anchor comprises: a tensioning pup adapted for engaging thetubing hanger for lifting the tubing hanger and tubing string suspendedtherefrom for tensioning the tubing string; means for measuring atensioning distance applied for tensioning the anchored tubing string;and a retainer adapted for re-engaging the tubing hanger in the wellheaddognut when the tubing string is in tension. Preferably, a tensioningpup is engaged with the tubing hanger for supportably lifting andlowering the tubing hanger and tubing string suspended therefrom, thetensioning pup being marked with a series of gradations at evenly spacedintervals for measuring the tensioning distance therewith. The hangerretainer is preferably a nut for threaded engagement with the top end ofthe tubing hanger. More preferably, the hanger nut has a circumferentiallocking face which engages a circumferential locking face formed in thedognut for rotationally locking the tubing hanger and tubing string fromrotation once tensioned.

Further, a method of tensioning a tubing string suspended in a wellboreis provided wherein the tubing string has an upper end at a wellhead anda lower end having a tubing anchor, the wellhead having a bowl forlockably supporting a dognut therein, the method comprising: supportingthe tubing string at the wellhead with the upper end of the tubingstring projecting from the wellhead; fitting the upper end of the tubingstring with a tubing hanger for suspending the tubing string therefrom,the tubing hanger having a threaded top end; fitting a dognut over thetop end of the tubing hanger, the dognut having a bore and a top endhaving a first circumferential locking face extending radially outwardsfrom the bore; releasing the tubing string at the wellhead; lowering thetubing hanger and the tubing string so as to engage the dognut in thewellhead bowl; continuing to lower the tubing hanger and tubing stringso that the top end of the tubing hanger is below the top end of thedognut by a tensioning distance, the lower end of the tubing stringbeing substantially at a target depth; setting the tubing anchor to fixthe position of the lower end of the tubing string at the target depthin the wellbore; pulling up the tubing hanger and tubing string at leastthe tensioning distance to tension the tubing string and expose the topend of the tubing hanger; engaging a hanger retainer having a secondcircumferential locking face extending radially outwards therefrom tothe top end of the tubing hanger for supporting the tubing stringtherefrom; aligning the first and second circumferential locking faces;and lowering the hanger retainer supporting the tubing hanger and tubingstring into the dognut for suspending the tensioned tubing stringtherefrom, the first and second circumferential locking faces beingmated together for preventing rotation of the hanger retainer within thedognut.

Preferably, a tensioning pup is engaged with the tubing hanger forsupportably lifting and lowering the tubing hanger and tubing stringsuspended therefrom, the tensioning pup being marked with a series ofgradations at evenly spaced intervals for measuring the tensioningdistance therewith. The hanger retainer is preferably a nut for threadedengagement with the top end of the tubing hanger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is an exploded schematic view of a tensioning tool according toan embodiment of the invention, the tool being adapted for use totension production tubing suspended from a tubing hanger, to removebuckling therein;

FIG. 1 b is a cross-sectional view according to FIG. 1 a, along sectionlines A-A, illustrating mating circumferential locking faces of a hangerretainer and a modified dognut;

FIG. 2 a-c are partial longitudinal sectional views of the tensioningtool according to FIG. 1, in use to tension the production tubing, andmore particularly,

FIG. 2 a illustrates a first step of engaging the tensioning toolaccording to FIG. 1 into a top end of a tubing string, the tensioningtool and tubing string being lowered to a predetermined position priorto fixing the position of the lower end of the production tubing;

FIG. 2 b illustrates a second step wherein the dognut has been lockedinto place in the wellhead and the production tubing is tensioned bylifting the tubing at a top end to position the tensioning tool at apredetermined position;

FIG. 2 c illustrates a third step wherein a hanger retainer carried onthe tensioning tool engages a modified dognut for locking the productiontubing into the tensioned position;

FIG. 3 is a longitudinal sectional view of the wellhead illustrating theengaged hanger retainer and modified dognut positioned in the wellheadfollowing tensioning of the production tubing suspended therefrom;

FIG. 4 a is a partial longitudinal sectional view according to FIG. 2 billustrating the second step in tensioning the tubing string;

FIG. 4 b is a partial longitudinal sectional view according to FIG. 2 cillustrating the third step in tensioning the tubing string; and

FIG. 4 c is a partial perspective sectional view according to FIG. 4 b.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1 a, an embodiment of a tensioning tool 1 comprises atubing hanger 2 from which production tubing (not shown) is suspended, atensioning pup 3, threadably connected to the tubing hanger 2, amodified dognut 4 positioned about the tensioning pup 3 and beingaxially moveable thereover and a hanger retainer 5, preferably a hangernut, positioned on the tensioning pup 3 and being axially moveable overthe tensioning pup 3.

In the preferred embodiment and in a connecting position, the hanger nut5 is threaded for operational engagement in a secured position with anupper, outer threaded surface 66 at the top end 6 of the tubing hanger2. The top end 6 of the tubing hanger 2 is sized to fit axially upwardlythrough the dognut 4 for exposing the outer threaded surface 66 abovethe dognut 4 for engagement with the hanger nut 5. When engaged, the nut5 may seat on a shoulder 16.

Further, the tensioning pup 3 is threaded at an upper portion 7,adjacent a top end 8 of the tensioning pup 3, for temporarily retainingthe hanger nut 5 thereon during connection of the tensioning tool 1 tothe tubing hanger 2. The tensioning pup 3 has a threaded portion 17adjacent a bottom end 18 for connection to a threaded bore 19 of thetubing hanger 2. The production tubing (not shown) is suspended from thetubing hanger 2.

As shown in FIGS. 1 a and 1 b, the hanger retainer 5 is machined with anradially outward extending outer circumferential locking face 11 aboutan upper outer edge 12. The dognut 4 is machined having an innercircumferential locking face 13 formed to extend radially outwards froman upper, inner edge 14. One embodiment of the locking faces 11,13 is aform of compatible spline having a variable radial extent to lockrelative rotation. Once the circumferential locking faces 11,13 areengaged, the hanger retainer 5 and dognut 4 are fixed to preventindependent rotation of the hanger retainer 5, and supported tubinghanger 2 and tubing string 20, within the dognut 4 and to suspend thetubing hanger 2 and string 20 from the hanger retainer 5, supported inthe dognut 4.

The tensioning pup 3 is conveniently marked along a length with a seriesof gradations 10 used to measure the amount of tension or stretchingapplied to the tubing string 20. Typically, the gradations 10 are markedin 1 inch intervals.

In Use

Having reference to FIGS. 2 a-c and in use, a tubing string 20 ofproduction tubing is lowered into the wellbore 21 to the final sectionof tubing 20 with the lower end of the string at about a target depth.The string 20 is hung in a wellhead 9 from slips (such as shorty slipsnot shown). The tubing hanger 2 is threaded onto the final piece oftubing 20. The dognut 4 is then set onto the tubing string 20 over thetubing hanger 2. The hanger nut 5 is temporarily suspended above thedognut such as by threaded connection to threads 7 at the top end 8 ofthe tensioning pup 3. A seal 15, typically an O-ring, is placed over thetensioning pup 3 for sealing between the tubing hanger 2 and the dognut4 when installed. The tensioning pup 3 is then threaded into internalthreads 17 in the tubing hanger 2.

The tensioning pup 3 and tubing string 20 are lifted to release andremove the slips (not shown), after which the tubing string 20 islowered. The dognut 4 is landed into the bowl in the wellhead 9 andpreferably that his time the dognut 4 is locked into place in thewellhead 9 by setting a plurality of dogs 22. The tubing string 20 isfurther lowered a tensioning distance (FIG. 2 a) as measured on theseries of gradations 10 on the tensioning pup 3. One approach is to markthe tensioning distance from 0″ as the top end 6 of the tubing hanger 2when the tensioning pup 3 is threaded thereto. For example, as thetensioning pup 3 is typically graded in 1 inch intervals, in order tostretch the tubing by 5 inches the tubing string 20 is lowered arelative tensioning distance from 0″ to the 5 inch gradation on thetensioning pup 3 as viewed above the top end 6 of the tubing hanger 2and relative to some datum such as the dognut 4.

A tubing anchor 30 is set at a lower end 31 of the tubing string 20 tofix the position of the lower end 31 of the tubing string 20 in thewellbore 21 at the target depth.

In the case of a rotationally actuated tubing anchor 30, the tensioningpup 3 is rotated to set the tubing anchor 30. It may be necessary,depending upon the type of tubing anchor 30 used to hold at least someof the torque on the tubing anchor 30 to keep the tubing anchor 30engaged with the wellbore 21 until the tensioning operation is completedor thereafter.

As shown in FIG. 2 b, and once the tubing anchor 30 has been set, thetubing string 20 is lifted or pulled up to stretch the tubing string 20suspended therefrom. The tubing 20 is pulled upwards the tensioningdistance and a further distance sufficient to expose the threaded topend 6 of the tubing hanger 2 through the dognut 4. The O-ring 15 andhanger nut 5, which is released from the threads 7 at the top end 8 ofthe tensioning pup 3, are pushed down to the dognut 4. The hanger nut 5is threaded onto the top end of the tubing hanger 2.

As shown in FIG. 4 a, the hanger nut 5 is tightened onto the tubinghanger 2, preferably until the hanger nut 5 is adjacent or stops againstshoulder 16 on the tubing hanger 2. Typically, at this point thecircumferential locking face 11 of the hanger nut 5 sit a small distanceof approximately ±4″ above the dognut 4. In other words the top end 6 ofthe tubing hanger 2 is slightly over-tensioned more than the tensioningdistance to facilitate engaging the hanger retainer. The outercircumferential locking face 11 of the hanger nut 5 is aligned to matewith the inner circumferential locking face 13 of the dognut 4.

As shown in FIGS. 2 c, 3 and 4 b-c, the tubing hanger 2 and string 20 islowered the last small distance downwards through the dognut 4,compressing the O-ring 15 to seal against the tubing hanger 2. Thecircumferential locking faces 11,13 on the hanger retainer or nut 5 andthe dognut 4 mate and act to rotationally lock the tubing hanger 2 intothe dognut 4, retaining at least some of the torque applied to thetubing string 20 in the case where rotation is used to set the tubinganchor 30 and to suspend the tubing string 20 from the hanger nut 5supported in the dognut 4. There may be some residual rotation of thetop end 6 of the tubing hanger 2 to seat the shoulder 16 into the hangernut 5.

Once the tensioning operation is completed, the pulling tool is removedand the tensioning pup 3 is unthreaded and removed from the tubinghanger 2 and such production equipment as is required is connectedthereto.

1. A tensioning tool for tensioning a tubing string suspended in awellbore casing by a tubing hanger supported in a dognut in a wellheadand anchored at a downhole end by a tubing anchor comprising: meansadapted for engaging the tubing hanger for lifting the tubing hanger andtubing string suspended therefrom for tensioning the tubing string;means for measuring a tensioning distance applied for tensioning theanchored tubing string; and means adapted for engaging the tubing hangerin the dognut when the tubing string is in tension.
 2. The tensioningtool as described in claim 1 wherein the means adapted for engaging thetubing hanger and for measuring the tensioning distance of the tubinghanger and anchored tubing string is a tensioning pup adapted forconnection to the tubing hanger at a lower end and a lifting means at anupper end, the tensioning pup having a series of evenly spacedgradations marked thereon for measuring the amount of tension applied tothe tubing hanger and suspended tubing string.
 3. The tensioning tool asdescribed in claim 1 wherein the dognut further comprises a bore forpositioning the dognut about the tensioning pup and being axiallymoveable thereon and having a profiled inner circumferential lockingface formed about an upper inner edge; and the means adapted forengaging the top end of the tubing hanger in the dognut comprises ahanger retainer adapted for engagement with the top end of the tubinghanger and having an outer circumferential locking face about an upperouter edge, wherein, in a secured position the hanger retainer is movingaxially over the tensioning pup for connection to engagement means atthe top end of the tubing hanger, the hanger retainer, tubing hanger andsuspended tubing being lowered into and engaged in the dognut forsupporting the tubing hanger and tensioned tubing therefrom and aligningand mating the circumferential locking faces of the hanger retainer andthe donut, preventing release of the hanger retainer from the dognut. 4.The tensioning tool as described in claim 3 further comprising: atemporary engagement means formed at an outer upper end of thetensioning pup; and wherein in a connecting position, the hangerretainer is temporarily engageable at the upper end of the tensioningpup by the outer engagement means during connection of the tensioningpup to the tubing hanger; and in the secured position, the hangerretainer is releasable from the upper end of the tensioning pup formoving axially thereover for connection to the engagement means at thetop end of the tubing hanger.
 5. The tensioning tool as described inclaim 4 wherein the engagement means at the outer upper end of thetensioning pup and the top end the tubing hanger are a plurality ofthreads formed thereon and the hanger retainer is threaded forengagement therewith.
 6. The tensioning tool as described in claim 1further comprising a seal formed about the hanger retainer for sealingbetween the hanger retainer and the dognut in the secured position.
 7. Atensioning tool for tensioning a tubing string suspended in a wellborecasing by a dognut supported in a wellhead, the tubing string beinganchored at a downhole end by a tubing anchor comprising: a tubinghanger having a top end movable through the dognut; a tensioning pupadapted at a lower end for supportable connection to the tubing hangerand tubing string suspended therefrom and adapted for connection to alifting means at an upper end for lifting the tubing hanger andsuspended tubing string for tensioning the tubing string; and a retainerfor engaging the top end of the tubing hanger in the dognut once thesubbing string is in tension.
 8. The tensioning tool as described inclaim 7 further comprising a series of gradations marked on thetensioning pup for measuring the amount of tension placed on the tubingstring.
 9. The tensioning tool as described in claim 7 wherein thedognut further comprises a bore for positioning the dognut about thetensioning pup and being axially moveable thereon and having a profiledinner circumferential locking face formed about an upper inner edge; andthe means adapted for engaging the top end of the tubing hanger in thedognut comprises a hanger retainer adapted for engagement with the topend of the tubing hanger and having an outer circumferential lockingface about an upper outer edge, wherein, in a secured position thehanger retainer is moving axially over the tensioning pup for connectionto engagement means at the top end of the tubing hanger, the hangerretainer, tubing hanger and suspended tubing being lowered into andengaged in the dognut for supporting the tubing hanger and tensionedtubing therefrom and aligning and mating the circumferential lockingfaces of the hanger retainer and the donut, preventing release of thehanger retainer from the dognut.
 10. The tensioning tool as described inclaim 9 further comprising: a temporary engagement means formed at anouter upper end of the tensioning pup; and wherein in a connectingposition, the hanger retainer is temporarily engageable at the upper endof the tensioning pup by the outer engagement means during connection ofthe tensioning pup to the tubing hanger; and in the secured position,the hanger retainer is releasable from the upper end of the tensioningpup for moving axially thereover for connection to the engagement meansat the top end of the tubing hanger.
 11. The tensioning tool asdescribed in claim 10 wherein the engagement means at the outer upperend of the tensioning pup and the top end the tubing hanger are aplurality of threads formed thereon and the hanger retainer is threadedfor engagement therewith.
 12. The tensioning tool as described in claim7 further comprising a seal formed about the hanger retainer for sealingbetween the hanger retainer and the dognut in the secured position. 13.A method of tensioning a tubing string suspended in a wellbore, thetubing string having an upper end at a wellhead and a lower end having atubing anchor, the wellhead having a bowl for lockably supporting adognut therein, the method comprising: supporting the tubing string atthe wellhead with the upper end of the tubing string projecting from thewellhead; fitting the upper end of the tubing string with a tubinghanger for suspending the tubing string therefrom, the tubing hangerhaving a threaded top end; fitting a dognut over the top end of thetubing hanger, the dognut having a bore and a top end having a firstcircumferential locking face extending radially outwards from the bore;releasing the tubing string at the wellhead; lowering the tubing hangerand the tubing string so as to engage the dognut in the wellhead bowl;continuing to lower the tubing hanger and tubing string so that the topend of the tubing hanger is below the top end of the dognut by atensioning distance, the lower end of the tubing string beingsubstantially at a target depth; setting the tubing anchor to fix theposition of the lower end of the tubing string at the target depth inthe wellbore; pulling up the tubing hanger and tubing string at leastthe tensioning distance to tension the tubing string and expose the topend of the tubing hanger; engaging a hanger retainer having a secondcircumferential locking face extending radially outwards therefrom tothe top end of the tubing hanger for supporting the tubing stringtherefrom; aligning the first and second circumferential locking faces;and lowering the hanger retainer supporting the tubing hanger and tubingstring into the dognut for suspending the tensioned tubing stringtherefrom, the first and second circumferential locking faces beingmated together for preventing rotation of the hanger retainer within thedognut.
 14. The method as described in claim 13 wherein the tubinganchor is set rotationally, further comprising: applying torque to thetubing string for setting the tubing anchor; maintaining at least someof the torque on the tubing string while tensioning the tubing string,engaging the hanger retainer in the dognut, wherein the mated first andsecond locked circumferential locking faces maintain the at least someof the torque by preventing rotation of the hanger retainer within thedognut.
 15. The method as described in claim 13, following fitting thedognut over the tubing hanger, further comprising: engaging a tensioningpup with the tubing hanger for supportably lifting and lowering thetubing hanger and tubing string suspended therefrom.
 16. The method asdescribed in claim 15 further comprising: lowering the tubing hanger atensioning distance by lowering the tensioning pup as measured against aseries of gradations at evenly spaced intervals along the tensioning pupfor measuring the relative tensioning distance.
 17. The method asdescribed in claim 16 wherein the gradations are spaced at one inchintervals.
 18. The method as described in claim 15 wherein thetensioning pup has outer engagement means formed at a top end fortemporarily retaining the hanger retainer thereon prior to engaging thehanger retainer with the tubing hanger.
 19. The method as described inclaim 18 wherein the hanger retainer is a hanger nut and wherein the topend of the tubing hanger is a plurality of threads for threadablyengaging the hanger nut thereon.